The present invention relates to cobalt metal agglomerates consisting of peanut-shaped primary particles, to a process for the production thereof and to the use thereof.
Finely divided cobalt metal is mainly used as a binder in the production of hard metal and cutting tools based on various hard materials, such as for example WC, diamond, SiC and CBN. The cobalt metals used, for example, in the production of diamond tools must fulfil specific requirements. These include, in the first instance, that impurities such as Al, Ca, Mg, S and Si should be avoided as these elements readily form stabile oxides with the residual oxygen of the cobalt metal powder, so causing unwanted porosity in the segments.
It is also necessary, especially when producing segments with synthetic diamonds, to use only cobalt metal powders with very active sintering properties, as minimum densities of 8.5 g/cm.sup.3 are required in this case. These densities should be achieved at a sintering temperature range of as low as &lt;900.degree. C. because the diamond may be converted into graphite at higher temperatures. If the sintering activity of the cobalt metal is inadequate, sufficient hardness is not achieved. Under the extreme stresses to which annular drilling bits or cutting tools are exposed, the abrasive action of stone dust leads to deep erosion and unwanted detachment of the diamonds or other hard materials and consequently a loss of cutting performance.
According to the prior art, cobalt metals are used, on the one hand, in the form of mixtures of atomised cobalt metal powders with hydrogen-reduced powders, as are disclosed in DE-A 4 343 594, on the other hand as ultra-fine and extra-fine grade cobalt metal powders.
Ultra-fine powders are differentiated by their FSSS value of &lt;1.0 .mu.m from extra-fine powders which have FSSS values of between 1.2 and 1.4 .mu.m.
The small particle size and the resultant large surface areas of the described cobalt metal powders promote the absorption of atmospheric oxygen and moisture, which frequently leads to degradation of the flowability of the powders.
The object of the present invention was thus to provide a sintering active cobalt metal which does not exhibit the stated disadvantages, but does allow the production of segments with elevated density and hardness.
It has now proved possible to provide a cobalt metal powder which exhibits these required properties.